1. Field of the Invention
The invention relates to cooking equipment and methods. More particularly, the invention concerns processing of grain, especially corn, for milling into a cohesive product suitable for forming a basic food product such as masa harina, which is a traditional corn flour used in preparing dough (masa) for making tortillas and the like. For domestic cooking, as well as certain commercial uses, it is desirable to provide a dry flour which with added water produces a dough of proper consistency and handling qualities. Lime is usually added for organoleptic purposes to give a final product which produces the proper taste and color.
2. History of the Prior Art
Corn is a staple food in Mexico and tortillas constitute the principal form in which corn is consumed in that country. The masa for tortillas is made by following a traditional cooking method involving hydrated lime (calcium hydroxide) heat treatment in which alkaline hydrolysis results by boiling corn grain in an aqueous solution. In the traditional procedure, corn is boiled for about twenty minutes in the lime solution, the mixture is allowed to stand overnight, the supernatant is decanted and the product is thoroughly rinsed with water. The wet corn product is then stone ground, giving the resulting masa product used to make tortillas. Optionally, for the convenience of a domestic user or for some commercial users, it is desirable to provide the dry flour, or instant tortilla flour, that is called masa harina. Certain known processes for making masa harina include U.S. Pat. No. 826,983, patented July 24, 1906 by Wreford et al, disclosing steeping corn in the traditional manner, followed by drying the kernels and grinding into flour. Erosa et al, in U.S. Pat. No. 987,560, patented Mar. 21, 1911, teach a process for partially boiling corn in calcium hydroxide solution and then grinding the wet kernels into paste. Water is pressed from the paste, followed by drying of press cake in a heated chamber, followed in turn by grinding into flour. A similar process is disclosed by Villegas in U.S. Pat. No. 1,262,144, patented Apr. 9, 1918, where the amount of lime in water is one-half per cent, and Garza in U.S. Pat. No. 1,334,366, issued Mar. 23, 1920, calls for molding of dough into small thin cakes which are dried and then ground into flour. A similar process is described by Lloyd in Pat. No. 2,584,893, issued Feb. 5, 1952.
Diez de Sollano et al in U.S. Pat. Nos. 2,704,257, issued Mar. 15, 1955; 2,854,339, issued Sept. 30, 1958; and 2,930,699, issued Mar. 29, 1960 disclose steeping of corn in calcium hydroxide solution at a temperature well below the gelatinization point of starch of the corn, followed by drying of the whole steeped corn in a hot airstream while simultaneously comminuting it to obtain a flour which has been dried at temperatures less than 74.degree. C. to a moisture content of not more than 10% by weight. The patents also describe apparatus for use in the drying and grinding steps.
The presence of lime (which is added before grinding), is more adverse in the prior art, because the lime reacts with the corn and dissolves some of it. The practice in the prior art is to use somewhat more lime than necessary, then seep off or rinse the wet product to remove the excess lime, which also removes the corn that was dissolved in the lime. As much as 5% loss can arise from this reason.
Other patents of interest for showing processes for treating grains include the following:
______________________________________ U.S. Pat. No. Patentee ______________________________________ 3,117,868 Madrazo et al 242,588 Boon 1,018,595 Villegas 1,061,933 Willford 1,221,636 Von Hagen 1,265,700 Von Hagen 1,268,860 De Lara 1,586,869 Wesener 2,585,978 Van Atta ______________________________________
Each of the processes described in these patents, however, require for making an instant flour, such as masa harina for preparing tortillas, that the corn or other grain be first boiled or steeped, such as in an alkaline solution, with subsequent removal of water absorbed into the grain so that a stable flour can be made having proper doughing characteristics when reconstituted by addition of water. Accordingly, these methods suffer from the disadvantage of cost involved in boiling and removing water, both in terms of time expended and fuel consumed. With rapidly escalating fuel costs and the need for energy conservation, such processes are falling increasingly into disfavor. Moreover, discarding excess water after boiling of the grain can constitute an environmental problem, with most states in the United States now requiring such water to be specially treated due to its biochemical oxygen demand.
Of interest to the general subjects only of drying apparatus and hammer mill devices are the following patents:
______________________________________ U.S. Pat. No. Patentee ______________________________________ 2,535,570 Gordon 2,509,418 Brown 2,152,367 Smith 233,341 Gaines 1,244,774 Pointe 2,587,372 Oliver 3,761,024 Schwey et al 2,873,663 Hawk et al 2,477,627 Lanter ______________________________________
Mendoza, in U.S. Pat. No. 3,983,261, patented Sept. 28, 1976, discloses a method of milling grain while simultaneously cooking the grain with apparatus employing a coaxial conical rotor and stator between which the grain is crushed into a kind of paste. Heat is applied which decreases the relative humidity and the process is disadvantageous in providing an inconvenient form of final product and requiring further drying to produce an instant type flour. The paste is about 40% water, which is then dried to a low level and the product is reground to obtain the desired flour.
It is accordingly a principal object of the invention to provide a method and apparatus for continuously processing grain into a dry flour suitable for preparing foodstuffs upon the addition of water.
Another object is to provide a process for treating grain by crushing the grain and thereby generating heat autogenously, separating the comminuted grain produced thereby under conditions of moist heat, and removing the flour for storage and later use.
Still another object is to provide a process for treating corn to provide a corn flour with a moisture content of between about 5% and 12% which needs no separate drying step
These objects, together with other objects and advantages which will become subsequently apparent, reside in the details of construction and operation as more fully hereinafter described and claimed. In the accompanying drawings forming a part hereof, like numerals refer to like parts throughout.